The state’s child welfare agency has intensified efforts to remove children from troubled homes since preschooler Jeremiah Oliver was reported missing in December, a dramatic shift that critics say has put more strain on an already overburdened system.

From December through May, the state Department of Children and Families filed nearly 2,000 court petitions to gain custody of children they determined to be at risk of abuse or neglect, a 52 percent increase from the previous year, according to court statistics. Last month, the agency filed 365 such petitions, a 70 percent jump from May 2013.

Child advocates say the surge marks a clear response to criticism of the agency following the Oliver scandal, which led to the resignation of commissioner Olga Roche in April. Many describe the jump in custody petitions as an overreaction to intense public scrutiny that will needlessly send more children into foster care.

“It’s symptomatic of an agency that is continuing to struggle,” Marylou Sudders, associate professor at Boston College Graduate School of Social Work, said Thursday. “You have line workers who, if there is any question, are going to default to the side of filing [for custody]. I think the entire agency is risk-averse.”

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With more children being taken from their homes, social workers are scrambling to place them in foster care. And with so many cases, lawyers who represent parents seeking to keep custody of their children are in short supply, and hearings cannot be heard within three days as legally required.

The focus on removing children from chaotic and potentially dangerous homes is not surprising, advocates say, given the intense public scrutiny the agency has faced since acknowledging that social workers had not visited Jeremiah Oliver’s family for several months before he disappeared. The boy’s body was found in April by the side of a highway in Sterling; his mother and her boyfriend have been charged in connection with the boy’s disappearance.

Other tragedies involving children have increased criticism of DCF, including a case that month in which the agency said it had misplaced a fax sent by Grafton police about the safety of a 1-month-old infant, who later died.

In a statement Thursday, DCF said that periods of “hypervigilance” typically follow high-profile cases, both within the agency and among police officers, teachers, hospital workers, and others who report abuse.

In January, Roche directed staff to investigate allegations of abuse or neglect involving children age 5 and under with parents who have a history of substance abuse, domestic violence, mental health issues, or “unresolved childhood trauma.”

“The safety and well-being of the Commonwealth’s children is our number one concern,” the agency said. “When an allegation of abuse or neglect comes to the department’s attention, we engage in a thoughtful and deliberative process to ensure a course of action that is in the best interest of the child.”

Peter MacKinnon, president of the union chapter that represents the state’s child welfare workers, said the increase in referrals to foster care is the product of “an atmosphere of extreme fear” that has trickled down from top management to caseworkers.

“No one wants to have the next Jeremiah Oliver on their caseload,” MacKinnon said. “It used to be that we would put services into the home. Now the service is foster care.”

DCF has also stepped up its investigations of abuse and neglect, increasing the burden on social workers, several advocates said.

High-profile deaths of children under state supervision typically spur a more cautious approach, at least in the short term. But this increase has been more pronounced and sustained, those who work with children say.

“Every few years there’s a crisis at DCF, and we go through this,” MacKinnon said. “But what’s different about the last six months is that it hasn’t slowed down.”

The increase in petitions filed to gain custody of children stands in marked contrast to recent years. Between 2008 and 2012, the number fell 30 percent, part of an effort to keep families together whenever possible.

In May, the state’s child advocate office cited that philosophy in a report concluding that DCF erred by leaving a Lynn infant in a deeply troubled home, where he was fatally beaten, allegedly by his mother’s drug-addicted boyfriend, in July 2013.

“Many felt that a shift in values had occurred and DCF was no longer taking custody of children when the agency should have done so and that children were remaining in their homes when they should have been removed to foster or kinship care,” the report found.

Under Roche, the agency sought a more balanced approach, advocates said. But Gail Garinger, the state’s child advocate, said the recent surge suggested the pendulum had swung too far in the other direction.

“Clearly a different lens is being used to determine whether court involvement is appropriate,” she said. Given the high threshold for taking custody, “one would hope there are no significant fluctuations in the number of petitions filed,” she said in an interview.

Since Jeremiah Oliver’s disappearance, social workers have taken a harder look at families already being monitored by DCF, especially families with young children. Since the death of the Lynn infant, who was born with drugs in his system, the agency has given sharper scrutiny to such cases, advocates said.

Judges, who traditionally give broad deference to the agency’s wishes, have also become more likely to remove children in recent months, advocates said.

Erin Bradley, executive director of Children’s League of Massachusetts, said the rise in young children in foster care further strains that system.

“We haven’t seen a spike like this with kids under 5 in years and years,” Bradley said. “All of my providers are maxed out.”

Bradley said that she expects DCF petitions to level off this summer, and that some of the increase was justified, a welcome recognition that too many children were being left in risky homes.

Susan Elsen — attorney for the Massachusetts Law Reform Institute, which keeps a close watch on DCF — said investigations of abuse and neglect climbed 67 percent between January and March.

But heavier caseloads make it harder for social workers to determine when parents can no longer safely care for their children and to work with troubled families to help keep them stable.

“It’s important that you don’t let these increases spiral out of control,” she said. “You want to avoid separating children from their families whenever possible.”

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